So I bottle my second kit and used a few growlers in the mix. Two of which I had already bottle with (plastic caps) with no problems. Third one was a new one I got second hand (metal cap with some foam to seal). I go down to chek on them after a little under a week and see a weird beer spray like arc around this third bottle. Looks weird and is not fresh because its already a little sticky. I touch around the cap assuming it blew its gasket (literally) and its dry, I go to pick it up and the bottom stays on the shelf, emptying 64 oz onto my socks.

Sounds like an uneven mix of priming sugar perhaps leading to an over charged growler (I will do the gentle stir while bottling technique next time.

Also the break was weird, it was like the bottom was cut off, almost a perfect line right around the very bottom of the jug, leaving a flat little glass dish behind (a little bit curved up on the edges).

Anyone seen this happen? Bad growler design? Defect? Should I return the other ones from the same brewery?

I was surprised the first time the bottom dropped out of a bottle, but the corner is a focus for stress. Also, you are more likely to have flaws, bubbles, etc. in the corners.

Sounds like you have a solution to poorly sealing growler caps, though.

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Yeah I've got mostly Sam Adams bottles, just much easier to clean a couple growlers instead of a dozen bottles.

I've heard about that 2 liter move and may do that for a batch made for a camping trip. Also going to keep some plastic 16 oz Miller Lite bottles sold at the store near me, I think they will work just like any reusable PET.